This invention relates generally to the formation of electrically conductive metal patterns and more particularly to the formation of aluminum/copper alloy conductor lands in integrated circuit manufacture.
In integrated circuit manufacture, metal interconnection systems of aluminum are employed. Copper in amounts of about 1 to 8 percent by weight is added to the aluminum in order to increase the electromigration resistance of the aluminum. In the past, layers of aluminum/copper alloys have been deposited and patterned either by lift-off techniques or by substractive wet etching. More recently, plasma etching techniques have been used to etch aluminum, for example, the reactive ion etching process described in U.S. Pat. No. 3,994,793. According to this process a silicon semiconductor wafer, having a layer of aluminum on a dielectric layer, is partially masked and the exposed aluminum is reactively ion etched in, for example, an atmosphere of CC1.sub.4 and argon. in etching alloys of aluminum, such as aluminum/copper or aluminum/silicon it is mentioned in the patent that substrate heating is advantageous. In fact, when attempting to etch aluminum/copper alloys, substrate heating is needed in order to obtan a satisfactory etching process because without substrate heating a residue forms which stops the etching process before it is completed. This heating requires the equipment capability to heat the substrate which can be expensive or difficult to retrofit on existing equipment.
U.S. Pat. No. 3,918,149 describes the formation of aluminum/silicon ohmic contacts while avoiding the problem of dissolution of substrate silicon which can cause shorting of the contact by depositing an additional layer of silicon on the substrate followed by a layer of aluminum. The aluminum is patterned by photomask and wet etching and then the exposed silicon is removed by plasma etching with freon gas to which the aluminum layer is resistant so that it acts as an etch mask. The remaining aluminum and silicon are then homogenized by heating to form an aluminum/silicon alloy contact to the silicon substrate without substantial dissolution of substrate silicon.